Questions about diffusion

I got some questions about diffusion. My note says that diffusion is affected by

1. Solubilty of solute- What do they mean by this. Does solubility increase or decrease the rate. Since water is the major liquid found inside the body. Are they referring to solubilty in water. If they are not soluble (non polar) can't they easily diffuse through the membrane. Or are they simply saying that less solubilty means less movement and less diffusion.
2. Concentration gradient- Atleast I understand this.
3. Number of H bonds to be broken- When dissolved in water do they have to break H bonds first before diffusing. I don't understand this.
4. Charge density of electrolytes- I understand why polar molecules would find it difficult to diffuse but not ions. Why would have an ionic charge make it difficult to diffuse?

I also have a question about osmosis and diffusion of ions. When water diffuses through the membrane, does the ions or anything dissolved in it diffuse as well. If so why do ions need specific protein channels for diffusion can't they just diffuse with water.